Three such incidents have so far been reported - all in the Torridge district of Devon.

The first, on January 28 , involved a silver MG ZS car, which has since been seized by police. Two subsequent reports, on February 6 and February 7 respectively, are said to have involved a black BMW 3-series car.

Torridge sector inspector Shaun Kenneally with a black BMW 3-series, similar to the one police wish to trace

The incident on February 7 in Northam Square saw a man sustain minor injuries in an attack police believe may have involved a knife.

Both the previous reports happened on roads between Torrington and Bideford.

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Insp Kenneally said the incidents were "very unusual" and understood if people felt worried about being stopped by the police.

He offered the following advice to motorists:

If anyone is unsure whether the car flashing them is the police, then do not stop.

If you are not 100% sure it is a genuine police car, drive the nearest police station or public place, such as a petrol station.

In remote areas, the driveway of a clearly occupied house could do at a push.

Do not to stop anywhere secluded.

If in doubt, call 999 - the police can always check if one of their cars is following you.

Even if you decide not to stop straightaway and have to wait for a safe place to pull over, motorists are advised to signal to the police car that you have acknowledged the request - perhaps by turning on your hazard lights.

Do not drive off at great speed making the police think you are trying to get away.